System and method for programming and controlling over current trip point limits in voltage regulators

ABSTRACT

A system and method for controlling an over current protection trip point for a voltage regulator includes an input for receiving a monitored operating parameter of the voltage regulator. Control logic responsive to this input generates a digital current control signal. A digital to analog controller converts the digital current control signal to an analog current control signal and this analog current control signal is used for controlling a current source for generating a current that establishes the over current protection trip point of the voltage regulator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.60/890,286, filed on Feb. 16, 2007, which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to voltage regulators, and moreparticularly, to a system and method for programming and controllingover current trip point limits within a voltage regulator.

BACKGROUND

The desire to increase the accuracy of over current protection (OCP)trip points has become of increased importance within the semiconductorindustry. OCP measurement accuracy has advanced to the point wherecircuit offsets are no longer the dominant factor in the OCP error stackup. Even with improvements to OCP performance, it is still notacceptable to many users who find that existing OCP solutions havesignificant variations and are only usable for short current protection.

The difference between a design with over current protection and adesign with short current protection is important. In a design with overcurrent protection, all critical specifications are met up to the pointthe regulator detects an over current event. One critical specificationin this regard is the maximum operating temperature of the voltageregulator. If an OCP trip point accuracy varies between 11 amps and 18amps as illustrated in FIG. 1, the voltage regulator would be rated fora 10 amp load yet it must be designed so that it can safely operate at18 amps without a thermal failure. Other failure modes, such as inductorsaturation, also must be designed for the higher current level. Thisrequires a designer to build extra margin and cost into their designs.As a result, users see an increase in over current protection accuracyas a real method to reduce their costs.

One present solution to this problem is for users to simply state thatthey have short current protection, where protection is only providedfor low impedance shorts that are detected before a thermal failureoccurs. While this works at times for low impedance shorts, intermediateshorts will not be detected prior to the regulator failing from thermaloverstress. There is a school of thought which believes that voltageregulators experiencing thermal overstress will increase theirtemperature and will naturally lower their OCP trip points. FIG. 1illustrates tests in this manner to exploit this, and even with thisaffect, a substantial variation in OCP trip points over temperature canbe seen.

Prior art voltage regulators use a fixed current source through a fixedresistor to program the over current protection limit. In these cases,there is a large variation on the OCP trip point as a function of inputvoltage and ambient temperature (see FIG. 1). Additional prior artimplementations use a programmable resistor whose values change withtemperature to compensate the OCP trip point. These designs typicallyutilize an NTC or PTC thermistor as appropriate. These solutions havenot obtained wide industry acceptance as external thermistors areexpensive and their temperature characteristics do not perfectly matchthe OCP trip point temperature variations for which they arecompensating. The solutions also do not compensate for other factorsthat affect the OCP trip point.

Thus, there is a need for a voltage regulator with a constant OCPthreshold as a function of temperature, input voltage and gate voltage.These variables are considered significant first and second order causesfor variation in the OCP trip point.

SUMMARY

The present invention, as disclosed and described herein, in one aspectthereof, comprises a system and method for controlling an over currenttrip protection point of a voltage regulator. Control logic generates adigital current control signal responsive to at least one monitoredoperating parameter of the voltage regulator. This monitored operatingparameter is received via a first input connected with the controllogic. A digital to analog converter generates an analog control signalfrom the digital control signal and this analog control signal is usedfor controlling a current source that generates a current to establishthe over current protection trip point of the voltage regulator.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to thefollowing description taken in conjunction with the accompanyingDrawings in which:

FIG. 1 illustrates the OCP trip point versus input voltage at varioustemperatures for prior art embodiments;

FIG. 2 is a block diagram of a DC/DC converter;

FIG. 3 is a schematic block diagram of a voltage regulator with a PWMconverter circuit;

FIG. 4 is a block diagram of a voltage regulator including controlcircuitry for adjusting the OCP trip point responsive to temperature;

FIG. 5 illustrates a voltage regulator for controlling the OCP trippoint responsive to various parameters which may also include thetemperature;

FIG. 6 illustrates a first embodiment for controlling the over currenttrip point of a voltage regulator;

FIG. 7 is a further embodiment of a circuit for controlling the overcurrent trip point in a voltage regulator using MOSFET RDSON for currentsense;

FIG. 8 illustrates yet a further embodiment of a circuit for controllingthe over current trip point in a voltage regulator using inductor DCR asa current sense element;

FIG. 9 is a flow diagram describing the operation of an over protectioncurrent IC using RDSON of high side MOSFET;

FIG. 10 is a flow diagram illustrating the manner for establishing theover current protection threshold; and

FIG. 11 is a chart illustrating the over current protection trip pointvs. temperature for high side over current with and withoutcompensation.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numbers are usedherein to designate like elements throughout the various views,embodiments of the present invention are illustrated and described, andother possible embodiments of the present invention are described. Thefigures are not necessarily drawn to scale, and in some instances thedrawings have been exaggerated and/or simplified in places forillustrative purposes only. One of ordinary skill in the art willappreciate the many possible applications and variations of the presentinvention based on the following examples of possible embodiments of thepresent invention.

FIG. 2 is a simplified schematic and block diagram of a DC to DCconverter 100. The DC to DC converter 100 is shown as a buck typeconverter for purposes of illustration, although it is understood thatthe present invention is equally applicable to other types of powerconverters. A pair of switches, Q1 and Q2, are coupled in series betweenrespective terminals of an input source voltage, shown as VIN, and powerground (PGND). In the embodiment shown, the switches Q1 and Q2 areimplemented in channel metal oxide semiconductor, field effecttransistors (MOSFETs), although other types of electronic switches arecontemplated including semiconductor switches suitable for integratedcircuit (IC) fabrication. The upper switch Q1 has its drain coupled toVIN, its gate receiving an upper gate control signal UGATE, and itssource coupled to the drain of the lower switch Q2 at a node PHASEdeveloping a PHASE signal. A node and the signal it develops arereferred to herein as the same unless otherwise specified. The lowerswitch Q2 having its drain coupled to PHASE, receives a lower gatecontrol signal LGATE at its gate and has its source coupled to PGND. ThePHASE node is coupled through an output inductor L to an output nodethat develops an output signal VOUT. The VOUT signal is applied to aload LD and an output capacitor CO both referenced to ground. The VOUTsignal is fed back through a feedback (FB) circuit 111 as a feedbackvoltage signal (VFB) to a controller 101, which outputs the UGATE andLGATE signals to control operation of switches Q1 and Q2. The PHASE nodeis also provided to the controller 101 for various purposes, includingover current detection.

The controller 101 includes an error amplifier 103, PWM logic 105, gatecontrol logic (GCL) 107 and the startup circuit 109. In typicalconfigurations, the error amplifier 103 senses VOUT via the VFB signalor a voltage sensed signal (not shown) or other means, and generates acompensation signal COMP provided at its output to the PWM logic 105. Asshown, VFB is provided to the inverting input of the error amplifier 103within the controller 101, although alternative methods are contemplatedfor sensing the output. The PWM logic 105 includes an oscillator or thelike (not shown) which generates a reference oscillation waveform and aPWM comparator which compares the reference wave form with the COMPsignal to generate a PWM wave form provided to the GCL 107. Based on thePWM signal, the GCL 107 asserts the UGATE signal high to turn on theswitch Q1 and asserts the LGATE signal low to turn off the switch Q2 tocouple VIN through the output inductor L to drive the voltage level ofVOUT. The GCL 107 then asserts the UGATE signal low and the LGATE signalhigh to turn off Q1 and turn on Q2. Operation toggles in this mannerbased on the duty cycle of the PWM signal.

A typical startup sequence is to ramp the reference signal provided tothe non-inverting input of the error amplifier 103 from zero to a setpoint voltage level. If VOUT is already pre-charged, such as by the loadLD or by the DC to DC converters, the VFB signal is already high and theerror amplifier 103 pulls COMP low. The PWM logic responds by producingthe PWM signal at a relatively low duty cycle causing the GCL 107 toactivate the lower switch Q2 for a substantial period of time in anattempt to reduce VOUT. Thus, the switch Q2 is coupled between groundand the pre-charged VOUT signal through the inductor L for asufficiently long enough period of time, potentially exceeding itsthermal limit. In general, if the average voltage across the inductor Lis not zero, surge currents are generated which potentially cause damageto the DC to DC converter 100 (e.g., the switch Q2) or to components inthe load LD.

The GCL 107 includes a pair of output drivers (not shown) that drive thegates of the switches Q1 and Q2 based on the PWM signal as known tothose skilled in the art. Also, the GCL 107 typically includes shootthrough protection logic or the like that ensures only one of theswitches Q1 and Q2 is on at any given time. When the enable signal isasserted high, the GCL operates as normal and when the enable signal isasserted low, the GCL turns both of the switches Q1 and Q2 off todisable output switching. In one embodiment, for example, the GCL 107disables both the output drivers so that the UGATE and LGATE signals areboth asserted low and remain low while the enable signal is assertedlow. Internal and external embodiments of the GCL 107 are contemplated.An external gate driver IC, for example, may be configured with anenable input that receives the enable signal or a version thereof. Insome embodiments, the GCL 107 tri states its outputs in response to theenable signal going low and a separate driver IC (not shown)incorporating the switches Q1 and Q2 detects the tri state condition anddisables itself. The present invention is not limited to any specificembodiment or configuration of the GCL 107 or the switching devices.While a single phase converter is described, multiphase converters mayalso be utilized.

Referring now to FIG. 3, there is illustrated a buck converter regulatorwith included PWM logic 105 and gate control logic 107 as discussed inFIG. 2. PWM comparator 208 has the output of the error amplifier 103applied to its positive input and its negative input connected toreceive an input from oscillator 206. The output of the oscillator 206is a triangular wave form. The output of the PWM comparator 208 isapplied to driver circuits 210 and 212 within the GCL circuitry 107,which drive the gates of the transistors 214 and 216 respectively. Thiscircuitry provides a pulse width modulated wave form with an amplitudeof V_(in) at a PHASE node 218 connected to a first side of inductor 220.The PWM wave form provided from PHASE node 218 is smoothed by an outputfilter consisting of inductor 220 and capacitor 222. The FB pinimpedance 111 comprises a compensation feed back loop for the erroramplifier 103.

The present system as illustrated in FIGS. 4 and 5 uses operatingparameters of the voltage regulator to compensate the over currentprotection trip point of a voltage regulator. Referring now moreparticularly to FIG. 4, a temperature sensor 402 is located proximal toa MOSFET switching transistor within the voltage regulator 404 to enablemonitoring of the temperature of the MOSFET switching transistor. Theinformation from the temperature sensor 402 is provided to a digitalcontroller 406 which generates control signals to adjust a digital toanalog controller (DAC) 408 The DAC 408 may comprise a current outputDAC or a voltage output DAC. The digital controller 406 and the DAC 408set the OCP trip point within the voltage regulator 404 so that the OCPtrip point is constant over the various temperatures detected by thetemperature sensor 402. Thus, the OCP trip point is constantly alteredresponsive to temperature indications provided by the temperature sensorenabling the provision of a constant trip point.

Referring now also to FIG. 5, there is illustrated an embodiment whereinthe voltage regulator 404 provides a plurality of sensed data signals tothe digital controller 406 such as temperature, input voltage, gatevoltage, etc. that may be used by the digital controller 404 to providecontrol signals to the DAC 408. The DAC 408 may comprise a currentoutput DAC or a voltage output DAC. Responsive to these sensed operatingparameter inputs of the voltage regulator 404, the DAC 408 maydynamically control the OCP trip point of the voltage regulator 404 toprovide a constant trip point over varying circuit conditions. Forexample, when using MOSFET RDSON for OCP monitoring, the MOSFET switchgate and source voltage can be monitored allowing the circuitry tocompensate the OCP trip point for variations in MOSFET RDSON as the gateto source voltage Vgs changes. Additionally, the input voltage can bemonitored and used to compensate for variations in the OCP trip point.Other variables can of course be monitored and compensated for as wellas would be well understood by one skilled in the art.

Referring now to FIGS. 6-8, there are illustrated various embodiments bywhich an integrated circuit 602 may be interconnected with the voltageregulator 604 to enable controlling of the over current protection trippoint within the voltage regulator 604. As can be seen from theimplementation in FIG. 6, IC controller 602 is connected across thehigh-side MOSFET 608 and the low-side of MOSFET 612 to the input voltagenode 606 the phase node 610 and the ground nodes respectively. In FIG.6, the input voltage VIN is applied to the voltage regulator 604 at node606. High-side MOSFET switching transistor 608 has its drain/source pathconnected between node 606 and the phase node 610 and the other endconnected to the output voltage modes. The low-side MOSFET switchingtransistor 612 is connected between the phase node 610 and ground. Aninductor 614 through which the load current IL passes has one endconnected to the phase node 610. A resistor 616 and a capacitor 618 areconnected in parallel between node 606 and the input pin HSOC 620 of theintegrated circuit 602. The over current threshold is generated at theHSOC 620.

The resistor 616 in parallel with the capacitor 618 provides severalbenefits to this implementation. Since the capacitor voltage is equal tothe voltage draw across the resistor 616, any change in the load currentIL will have an RC settling time which in turn allows for added control,using the value of the resistor 616 and the capacitor 618, on thebandwidth of the temperature compensating mechanism outside of thecontrol algorithm provided by a digital controller 622 within the IC602. The capacitor 618 also provides a fundamental method to smooth overcurrent protection threshold variations and nonlinearities introducedwithin the switches of the digital to analog controller (DAC) 624, whichmay typically have 6 bit resolution; however, other resolutions may beused, controlled by the digital controller 622. This simplifies thedesign of the digital to analog controller 624 and the controlcomplexity. The capacitor 618 also allows the use of a switchedcapacitor comparator design inside of the integrated circuit 602 as thecapacitor 618 provides the necessary filtering these types of circuitsrequire. Finally, the capacitor 618 is used as a high pass filter toallow the input voltage steps (due to the ESR in the input bulkdecoupling capacitors) to be passed to the HSOC pin 620, which wouldotherwise cause offsets and thus errors in the measurements.

Within the integrated circuit 602 in addition to the digital controller622 and 6-bit DAC 624 are included a current sink 626 and a currentsense circuit 628. The current sense circuit 628 generates an outputsignal that is provided to the PWM controller 101 (FIG. 2) that is usedto turn off the MOSFETS 608 AND 612 if the current on one MOSFET ishigher than the OCP threshold. The current sense circuit 628 isconnected between the HSOC pin 620 and the phase pin 630. External tothe IC 602 the phase pin 630 is connected to the phase node 610 of thevoltage regulator 604. The current sink 626 is connected between theHSOC pin 620 and the ground pin 632. The sink current source 626 iscontrolled by the 6-bit digital to analog converter 624 which assists inestablishing the OCP trip point responsive to control signals providedfrom the digital controller 622. The digital controller 622 wouldinclude various inputs 634 for receiving sensor data such astemperature, gate to source voltage, input voltage, etc., to enableestablishment of the constant trip point. Thus, the OCP trip pointlevels will be controlled by the digital controller 622 responsive tothe monitored sensor data provided at input 634. The digital controller622 programs the 6-bit DAC 624 to establish a DAC current 626 toestablish the desired trip point. In alternative embodiments the DAC 624can also be used to establish a DAC voltage. The current sensor 628measures a voltage drop across high side MOSFET 608. This is used todetermine the current through the high side MOSFET 608.

The design of the 6-bit (DAC) 624 requires several factors to be takeninto account. A 100 microamp nominal level is used as a reference inthis implementation. Fundamentally, the DAC 624 must have a sufficientrange to provide for all the variations that will be compensated for inthen voltage regulator, and the DAC 624 should provide good granularitythroughout this range. The DAC 624 range should be able to compensatefor the thermal variation of RDSON in each MOSFET. Over the industrialtemperature range, this equates to a +/−40% variation, or a range of 60microamps to 140 microamps. Additionally, part to part variation doesoccur from MOSFET vendors, and as such, additional margin has been builtinto the DAC 624 range to allow for set point trimming should a userwish to eliminate this source of error. In the implementation of FIG. 6,the DAC range is 50 microamps to approximately 197.7 microamps.Alternatively, an equivalent voltage range can be provided. Thisprovides approximately 17 point set point adjustment on top of the 40%variation.

The step size of the digital to analog controller 624 can also be variedby the digital controller 622. In a non-linear DAC where each step is afixed percentage greater than the last minimized set point error, thiscan cause other difficulties not the least of which is the impact on thealgorithm that must choose what DAC code to use for a given temperature.To ease algorithmic design and the fundamental DAC design, a 6-bitlinear DAC is utilized in one embodiment. This provides for loweraccuracy at low currents as compared to higher currents. However, theimplemented performance is considered acceptable. One reason is that theabove thermal augment which is insufficient for overall protection canbe applied in a reduced extent to enable the operation of the circuit tobe biased towards higher temperatures equating to higher RDSONs, andthus indicating that the most accuracy would be beneficial at higher DACcurrent values. In the implementation of FIG. 6, the DAC ranges from 50microamps to 197.7 microamps with an LSB with approximately 2.3microamps.

An additional implementation would monitor the gate to source voltage ofthe MOSFET 608 to allow for variations in RDSON due to this variable.Since the RDSON value depends on both the temperature of the MOSFET aswell as its gate to source voltage, the gate to source voltage can bemeasured either directly or by monitoring the MOSFET gate driver supplyvoltage and may then apply a correction on the over current limitvoltage using a DAC. Additionally, the monitored input voltage could beused to compensate the OCP threshold.

Referring now to FIG. 7, there is illustrated an alternative embodimentwherein the trip point controller IC 602 is connected to the voltageregulator 604 in a different configuration. In this case, the ICcontroller 602 has a phase pin 630 connected to the phase node 610 ofthe voltage regulator 604. An ISENSN pin 702 is connected to node 704 ofthe low-side MOSFET 612 at the ground node. The controller 602 alsoincludes a low-side over current pin (LSOC) 706 and a ground pin 708 andperform similar functions as described previously. The over currentthreshold is generated at the LSOC 706. The parallel combination of theresistor 616 and the capacitor 618 are connected between the LSOC pin706 and the ground pin 708. The digital controller 622 still programsthe DAC 624 responsive to received input operating parameter signalsfrom the voltage regulator 604. The DAC 624 controls the current source626 which provides a current to the LSOC pin 706 through node 710.Alternatively, as discussed previously, a voltage source could becontrolled. The current sensing circuit 608 is connected to the phasepin 630, ISENSN 702, ground pin 708 and LSOC pin 706 through node 710 tosense the current of the voltage regulator 604 passing through low-sideMOSFET 612. The current is determined based upon a voltage drop acrossthe low-side MOSFET 612. The voltage regulator 604 consists of thehigh-side MOSFET switching transistor 608 connected between the inputvoltage VIN and node 610; the low-side switching MOSFET transistor 612connected between the phase node 610 and the ground node 704 and aninductor 614 having one end connected to the phase node 610.

Referring now also to FIG. 8, there is illustrated yet a thirdembodiment of the manner for interconnecting the over current trip pointcontroller IC 602 with the voltage regulator 604. The voltage regulator604 consists of the high-side MOSFET 608 connected between the inputvoltage VIN and the phase node 610. The low-side switching transistorMOSFET 612 is connected between node 610 and ground. The inductor 614 isconnected between the phase node 610 and node 802. Resistor 804 isconnected between node 802 and the output voltage node 806 of thevoltage regulator 604. A resistor 808 and a capacitor 810 are connectedin series between the phase node 610 and the output voltage node 806.The resistor 808 is connected between the phase node 610 and node 812.The capacitor 810 is connected between node 812 and the output voltagenode 806. The over current protection IC 602 is connected with thevoltage regulator 604 through nodes 812 and the output voltage node 806.An ISENSP pin 814 connects to node 812. An ISENSN pin 816 connects tothe output voltage node 806. The parallel combination of the resistor616 and capacitor 618 are connected in parallel between the LSOC node706 and the ground node 708 to perform the functions describedpreviously. The over current threshold is generated at the LSOC 706. Thedigital controller 622 receives monitored parameters from the voltageregulator 604 via pin 634 as described previously and generates controlsignals to the DAC 624. The DAC 624 controls a source current 626 whichis provided to the LSOC pin 706. A current sensed circuit 628 detectsthe current through the inductor 614 based on the voltage drop acrossthe inductor and is connected to the ISENSP pin 814, ISENSN pin 816, theground pin 708 and the LSOC pin 706 through node 710. The RC circuitconsisting of resistor 616 and capacitor 618 in addition to beingconnected to ground may also be connected to V_(out) in an alternativeembodiment.

Referring now to FIG. 9, there is illustrated a flow diagram describingthe operation of the over current protection IC 602. Initially adetermination is made of the high-side MOSFET output current at step902. Next, inquiry step 904 determines if the voltage drop is occurringon the high-side MOSFET. If not, control passes back to step 902. If avoltage drop is occurring on the high-side MOSFET, the voltage drop onthe HSOC pin is determined at step 906. Based upon the voltage at theHSOC pin inquiry step 908 determines if the over current protectionthreshold limit has been exceeded. If not, control passes back to step904. If inquiry step 908 determines that the over current protectionthreshold limit has been exceeded the regulator is shut down at step910.

FIG. 10 is a flow diagram illustrating the manner in which the overcurrent protection IC 602 establishes the over current protectionthreshold. At step 1010, the temperature associated with the MOSFETRDSON or other parameters such as the gate voltage are measured. Next,this measured temperature or parameter information is used to generatecontrol data at step 1015 within the digital control circuit 622 of theIC 602. This digital control information is used to program the digitalto analog converter 624 at step 1020. The output of the digital toanalog controller is then used to control the generation of the overcurrent protection limit at step 1025.

Referring now to FIG. 11, there is illustrated a chart describing theover current protection (OCP) trip point versus temperature forhigh-side over current without compensation as illustrated by line 1102.As can be seen, without the compensation of the over current trip pointthere is a wide variation over temperature from minus 40 degrees toabove 80 degrees. When compensation of the V4 type is used asillustrated at 1104, the amount of variation in the OCP trip point isgreatly minimized. Likewise, when high-side over current limits with V3compensation as illustrated generally 1106 are used, the variations inthe OCP trip point are again limited. Thus, the use of the describedimplementation provides a dramatic improvement in OCP accuracy. Atpresent, OCP accuracy can vary up to 50% due to temperature factorsalone as illustrated by 1102 in FIG. 11. This methodology significantlyimproves accuracy by compensating for this error resulting inimprovements such as those illustrated at 1104 and 1106. Additionally,the methodology can be extended to compensate for other parameters thataffect the OCP trip point accuracy such as MOSFET gate to source voltageand input voltage variations.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that this invention provides an improved system andmethod of setting an over current protection trip point. It should beunderstood that the drawings and detailed description herein are to beregarded in an illustrative rather than a restrictive manner, and arenot intended to limit the invention to the particular forms and examplesdisclosed. On the contrary, the invention includes any furthermodifications, changes, rearrangements, substitutions, alternatives,design choices, and embodiments apparent to those of ordinary skill inthe art, without departing from the spirit and scope of this invention,as defined by the following claims. Thus, it is intended that thefollowing claims be interpreted to embrace all such furthermodifications, changes, rearrangements, substitutions, alternatives,design choices, and embodiments.

1. An apparatus for dynamically controlling an over current protectiontrip point for a voltage regulator, comprising: a first input forreceiving monitored changes in at least one operating parameter otherthan an output voltage of the voltage regulator; a digital controllerfor generating a digital control signal to set the over currentprotection trip point at a substantially constant level responsive tothe changes in the at least one operating parameter of the voltageregulator, the over current protection trip point establishing a pointfor shutting down the voltage regulator when a load current exceeds theover current protection trip point; and a digital to analog converterfor generating an analog control signal to set the over currentprotection trip point at the substantially constant level responsive tothe digital control signal.
 2. The apparatus of claim 1, furtherincluding a current sensor for measuring a current through a portion ofthe voltage regulator.
 3. The apparatus of claim 2, further including anRC circuit associated with the current sensor for providing additionalbandwidth control of the apparatus.
 4. The apparatus of claim 2, furtherincluding an RC circuit associated with the current sensor for smoothingover current protection trip point variations introduced by switching ofthe digital to analog converter.
 5. The apparatus of claim 2, furtherincluding an RC circuit associated with the current sensor for providinghigh pass filtering.
 6. The apparatus of claim 1, wherein the at leastone operating parameter comprises a temperature related to a switchingtransistor of the voltage regulator.
 7. The apparatus of claim 1,wherein the at least one operating parameter comprises a gate to sourcevoltage of a switching transistor of the voltage regulator.
 8. Theapparatus of claim 1, wherein the at least one operating parametercomprises an input voltage of the voltage regulator.
 9. The apparatus ofclaim 1, further including a current source responsive to the analogcontrol signal for establishing the over current protection trip point,further wherein the over current protection trip point established bythe current source remains substantially constant over variations in theat least one operating parameter.
 10. A system comprising: a voltageregulator for generating a regulated output voltage responsive to aninput voltage, the voltage regulator including a high-side switchingtransistor and a low-side switching transistor; an integrated circuitfor maintaining an over current protection trip point at a substantiallyconstant level for the voltage regulator, responsive to changes in atleast one monitored parameter of the voltage regulator, the integratedcircuit further including: a digital controller for generating a digitalcontrol signal to set the over current protection trip point at asubstantially constant level responsive to the changes in the at leastone operating parameter of the voltage regulator, the over currentprotection trip point establishing a point for shutting down the voltageregulator when a load current exceeds the over current protection trippoint; a digital to analog converter for generating an analog controlsignal to set the over current protection trip point at thesubstantially constant level responsive to the digital control signal;and a current source responsive to the analog control signal forestablishing the over current protection trip point, further wherein theover current protection trip point established by the current sourceremains substantially constant over variations in the operatingparameter.
 11. The system of claim 10, wherein the at least onemonitored parameter comprises a temperature related to at least one ofthe high-side switching transistor and the low-side switchingtransistor.
 12. The system of claim 10, wherein the at least onemonitored parameter comprises a monitored gate to source voltage of atleast one of the high-side switching transistor and the low-sideswitching transistor.
 13. The system of claim 10, wherein the at leastone monitored parameter comprises an input voltage of the voltageregulator.
 14. The system of claim 10, further including an RC circuitassociated with a current sensor.
 15. A method for controlling avariable over current protection trip point of a voltage regulator,comprising the steps of: monitoring at least one operating parameterother than an output voltage of the voltage regulator; generating adigital current control signal responsive to the at least one monitoredparameter of the voltage regulator; converting the digital currentcontrol signal to an analog control signal; and generating the overcurrent protection trip point at a substantially constant levelresponsive to the analog control signal, the over current protectiontrip point establishing a point for shutting down the voltage regulatorwhen a load current exceeds the over current protection trip point. 16.The method of claim 15, wherein the step of generating the over currentprotection trip point further includes the steps of: generating acontrol current responsive to changes in the analog control signal; andgenerating the over current protection trip point responsive to thecontrol current, wherein the over current protection trip pointestablished by a current source remains substantially constant overvariations in the operating parameter.
 17. The method of claim 15further including the step of measuring a current through a portion ofthe voltage regulator.
 18. The method of claim 15, wherein the step ofmonitoring further comprises the step of monitoring a temperaturerelated to a switching transistor of the voltage regulator.
 19. Themethod of claim 15, wherein the step of monitoring further comprises thestep of monitoring a gate to source voltage of a switching transistor ofthe voltage regulator.
 20. The method of claim 15, wherein the step ofmonitoring further comprises the step of monitoring an input voltage ofthe voltage regulator.